[en] Techniques are described that are used for neutron energy spectrometry of beams of intermediate energy neutrons being set up for boron neutron capture therapy (BNCT) research. These include high resolution proton and alpha recoil spectrometry (in the energy range from 10 keV to 15 MeV), activation detectors and spectrum modification using a variety of scattering materials. As an example, results of measurements made recently on the HB11 filtered beam in the JRC, Petten, High Flux Reactor (HFR) are given. The total fluence rate in this beam (determined from activation detector measurements) is 4.95 x 10⁸ cm^-1.s^-1, which corresponds to a neutron kerma rate in tissue of 1.59 Gy.h^-1. In the energy range above 10 keV, the fluence rate is only 0.912 x 10⁸ cm^-1.s^-1 (about a fifth of the total), but corresponding to over 92% of the total neutron kerma rate in tissue. Consequently, these measurements highlight the importance of making high resolution spectrum measurements using recoil counters for BNCT beams. (author)

[en] This paper reviews techniques, developed at Harwell Laboratory over the last few years, for determining the neutron and gamma-ray characteristics of intermediate energy neutron beams developed for Boron Neutron Capture Therapy (BNCT) experiments. They have been used for the characterization of several such beams: the iron/aluminium/sulphur and aluminium/sulphur/liquid argon beams developed at Harwell, the Petten High Flux Reactor (HFR) HB7 developmental beam and, most recently, the HFR HB11 beam. The techniques discussed include those for neutron spectrometry, beam profiling and gamma-ray dosimetry

[en] Single- and multi-element CR-39 dosemeters, developed at the Harwell Laboratory, and a commercially available multi-element CR-39 dosemeter (obtained from Track Analysis Systems Ltd), were evaluated for their potential as neutron dosemeters for personnel working at Harwell Laboratory's research reactors. Owing to the angular dependence of the CR-39 (processed using electrochemical etching), the single-element dosemeter was found to be impractical. Consequently, a multi-element dosemeter was developed, which consisted of a cube of side 36 mm with CR-39 elements (also processed using electrochemical etching) attached to each of the sides. Although this dosemeter was technically suitable for this type of dosimetry, it was considered to be unacceptably bulky in personnel trials. The commercially available CR-39 dosemeter tested was much smaller (the CR-39 was only chemically etched) and this was considered to be acceptable as a personnel dosemeter. In addition, trials with personnel working at active handling glove boxes indicated that single-element dosemeters might be adequate, but further work would be needed to verify this. (author)

[en] Neutron spectrometry measurements have been made in the working environments of three UK Nuclear Electric Magnox power stations, and of a PWR at Gosgen, Switzerland, using a high resolution spectrometry system based on high sensitivity cylindrical proton recoil counters and an alpha recoil counter. Multispheres were used to obtain dose equivalent information below the lower energy limit (∼ 50 keV) of the recoil counter system. The derived H*(10) spectra show that, in general, the dose equivalent arises mainly from neutrons in two energy regions: thermal to 10 eV; and 10 keV to 1 MeV, although in certain situations a major contribution may arise from thermal neutrons. Quality factors for the H*(10) dose equivalent are derived and compared with the proposed ICRP 60 (1990) radiation weighting factors. The measured spectra are also interpreted in terms of the response of several individual (personnel) dosemeters and survey instruments. (author)

[en] Three techniques, developed at the Harwell Laboratory, for separating thermoluminescent glow curves into their individual glow peaks are described. They are: non-linear least squares fitting; division of glow curves by a reference glow curve; and glow curve substraction. Using the non-linear least squares fitting method it becomes difficult to resolve individual glow peaks accurately from complex glow curves. The glow curve division method enables rapid evaluation of the relative intensities of the individual peaks relative to the corresponding peak intensities in the reference glow curve. Finally, given peak parameters determined by the previous two methods, dominant peaks can be successively subtracted to reveal the less dominant glow peaks for further analysis. As examples of the application of these methods, glow curves obtained in previous experimental work at Harwell have been analysed. These show the effect of LET and the effect of a pre-irradiation heat treatment on the individual glow peaks. (author)

[en] Three complementary techniques for thermoluminescence glow curve analysis have been developed at the Harwell Laboratory. These are: non-linear least squares fitting using Podgorsak's approximation for first-order kinetics; glow curve division, which involves dividing glow curves by a reference, well characterised, glow curve; and glow peak stripping. These techniques have been used to determine the sensitivity of individual glow peaks (4 - 10) in the ⁷LiF TLD chips (TLD-700) as a function of gamma ray dose in the range 10 mGy to 20 kGy. Glow curves obtained from normal readout (linear rise in temperature with time at 1⁰C.s^-1 up to 374⁰C) and from glow curves obtained after normal readout up to 300⁰C followed by UV phototransfer (UVPT) have been analysed. The techniques developed for glow curve analysis are summarised and results presented for the dose response of individual glow peaks obtained from normal and UVPT readout. The results show that the onset of supralinearity occurs at lower doses for peaks with higher peak temperatures. However, the dose at which the peaks saturate is independent of the peak. Finally the implications of these results for models of supralinearity and saturation are discussed. (author)

[en] Neutron spectra inside the containment building of a PWR at Gosgen, Switzerland have been measured using a high resolution, transportable, neutron spectrometry system based on proportional counters. Small spherical proportional counters, filled with hydrogen to pressures of 100, 300 and 1000 kPa, were used to cover the energy range from 50 keV to 1.5 MeV. A larger cylindrical counter, filled with 600 kPa of ⁴He plus 400 kPa Ar was used to extend the measurement range up to 16 MeV. Compact electronics provided simultaneous data acquisition for up to four counters allowing spectrum measurements to be performed in dose equivalent rates down to ∼ 50 μSv · h^-1. Supporting measurements were made with a multisphere spectrometer to determine the fraction of neutrons below 50 keV. The neutron spectra measured at two positions show a steady rise in the neutron fluence as the neutron energy decreases, with very few neutrons having energies above 700 keV. (author)

[en] Published in summary form only

[en] A computer program CRISIS (CRIticality asSiStant) has been developed, using an expert system language, to provide dose assessments for personnel following a criticality incident. The program has been designed to obtain the best dose estimates based on progressive measurements from individual (personnel) accident dosemeters, installed dosemeters and body sodium activation measurements. It provides an overview of an incident, including an estimate of the fission yield, and, by using in-built rules, tries to resolve the conflicts and anomalies which are certain to arise in interpretation. CRISIS is written in an object-oriented language, which includes rule-based reasoning and functional programming, which has the advantage of being able to use objects to model the incident more naturally. The program is run under WINDOWS-3 on an IBM compatible PC with a hard disk, although it could be made available for some other computer systems. CRISIS is not intended to replace the expert; rather it should be viewed as a knowledgeable assistant in the complex field of dose assessment, thus freeing the expert to concentrate on the relevance of the results. (Author)

[en] The response of CR-39 plastic to monoenergetic neutrons when irradiated behind several different radiators has been studied using conventional pre-etching, followed by electrochemical etching, to reveal tracks as enlarged spots. The effects of varying the electrochemical-etching voltage and pre-etching time were also investigated. It was found that to produce a low-energy neutron response the electrochemical-etching voltage must be greater than about 30 kV cm^-1. A short pre-etching time was found to give the lowest background. The influence of the radiators can be qualitatively understood in terms of contributions from elastic H(n,n)p collisions and (n,p) and (n,α) reactions in the radiator materials. (author)